1. Field of the Invention
This invention relates to the use of nonionic surfactants which are liquid at ambient temperature and have an HLB value of from 2 to less than 13, preferably from 2 to less than 12, for preventing the fogging of plastic surfaces.
2. Discussion of Related Art
It is known that numerous individual droplets are formed very easily from water vapor, for example on packaging films of flexible PVC, but do not coalesce to form a continuous film of water. In the case of flexible PVC films, for example of the type used for the packaging of fresh meat or fresh fruit, U.S. Pat. No. 3,479,308, France 1,569,130 and Japan 75 40 643, 79 86 545 and 78 69 247 describe various solutions to this problem by using highly ethoxylated sorbitan monooleates for example as so-called anti-fogging agents. However, this solution cannot be applied to plastic glazing in greenhouses, on terraces or the like.
From the considerably increased formation of water droplets on surfaces or, or even inside, double-walled sheets of polymethylmethacrylate or polycarbonate compared with glass, the permeability to light of plastic glazing of the above-mentioned polymers is considerably reduced so that plant growth in greenhouses is impaired. Fogging by water droplets is also aesthetically unattractive, and the falling of droplets onto the petals of delicate cultivated plants can lead to unwanted staining.
There has been no shortage of attempts in the past to solve the problem of fogging of plastic glazing. It has mainly been proposed in this regard that the surface of the plastic glazing be provided with a firmly adhering, film-forming coating, cf. German 31 29 262, European 149,182 and the earlier prior art cited therein.
However, the application of a coating which can be readily wetted with water requires a separate operation. In addition, in the case of double-walled sheets for example, the surfaces of the hollow interior would be virtually impossible to coat.